1. Field of the Invention
The present invention relates to a radio communication control device, a radio communication control system, a radio communication control method, a radio communication control program and a recording medium, which in particular, are capable of removing an interference source.
2. Description of Related Art
A W-CDMA (wide-band code division multiple access) system, a so-called third generation (3G) mobile communication system is providing high-speed communications through additional technologies such as a HSDPA (high-speed downlink packet access) technology. In an attempt to provide even faster communications, a new radio system called an LTE (Long Term Evolution) has been considered in a 3GPP (3rd Generation Partnership Project). With respect to the radio access system in the LTE, a SC-FDMA (single-carrier frequency division multiple access) scheme is adopted for uplink communications, whereas an OFDMA (orthogonal frequency division multiple access) scheme is adopted for downlink communications. The OFDMA is a digital modulation demodulation scheme by which multiple carrier waves (which are referred to as sub-carriers) are to be multiplexed using orthogonality of frequency. The features of the SC-FDMA resemble those of the OFDMA. What is different about the SC-FDMA from the OFDMA is that the carriers allocated to users are continuous in the SC-FDMA.
FIG. 7 is a diagram for explaining uplink radio resources (according to SC-FDMA technology) which are to be provided in the LTE system. As mentioned earlier, the SC-FDMA uses multiple carriers. These carriers correspond to the blocks present along the frequency axis as shown in FIG. 7. The radio resources are further divided along the time axis. In this way, blocks divided by frequency and time components are to be allocated to respective users. Blocks which are adjacent each other in frequency components can be allocated to a user. For example, at time t1, two blocks can be allocated to a user 3. The frequency components allocated in this case should be continuous as f1 and f2.
Japanese Patent Laid Open Publication No. 2003-018091, (cf. paragraphs 0002 to 0006) notes that interference will occur between adjacent base stations when they share the same frequency band in conducting modulation based on an OFDM (orthogonal frequency division multiplexing) system, and it further makes mention about conducting power control in order to resolve the interference problem between adjacent base stations and improve frequency utilization efficiency. Moreover, Japanese Patent Laid Open Publication No. 2004-159345, (cf. paragraphs 0002 to 0011) refers to a case of adjacent base stations allocating the same frequency resources to users.
For instance, in a case there is a user terminal a (4) under two base stations (base station 1 and base station 2), the base stations and the user terminal a (4) are under the condition of using the above-mentioned radio resource blocks allocation control and radio resource (see FIG. 8). As shown in FIG. 8, the user terminal a (4) is in a subordinate cell under the base station 1. On the other hand, the user terminal a (4) is also an uplink interference source for the base station 2. Furthermore, the user terminal a (4) is positioned outside a subordinate cell under the base station 2. Such relationship is identified as intercell interference occurring with respect to the base station 2. Here, as shown in FIG. 9, in a case when a user terminal b (5) is in a subordinate cell under the base station 2 which controls radio resource management (radio resource blocks allocation control), the user terminal a (4) uses higher transmission power than the user terminal b (5) considering possible propagation loss (or path loss) from the base station 1. Therefore, the interference to a signal of the user terminal b (5) will be brought to a level that can no longer be disregarded, whereby the base station 2 will need to inform the base station 1 that interference is occurring at frequency f1.
In this connection, document R1-073674 (“Overload Indicator handling for LTE” (3GPP), Nokia Siemens Networks, Nokia, internet source: URL: http://www.3gpp.org/ftp/Specs/html-info/TDocExMtg--R1-50--26036.htm) contributed to the 3GPP RAN1 Working Group indicates that introduction of an OI (overload indicator, also referred to as interference notification signal, in general) is being discussed in the 3GPP. The OI is a signal generated between base stations to indicate an occurrence of intercell interference. In a case described with reference to FIG. 9, the operation of the OI corresponds to the operation of the base station 2 informing the base station 1 about the occurrence of interference at frequency f1. Moreover, Japanese Patent Laid Open Publication No. 2005-065182, (cf. paragraphs 0011 to 0013) refers to a case of a base station detecting as to whether there is a different base station having a communication area that overlaps with its own communication area, and notifying the detected base station with the possibility of radio wave interference if there is any.
The OI contains frequency information where interference has been found. Based on this information, the notified base station is able to speculate that the user terminal using the designated frequency is the source of interference. The base station having received the OI will restrict radio resource allocation with respect to the user terminal of the interference source in order to let the user terminal use frequency other than the one designated, and thus reduce the interference with respect to the adjacent base station.